Improve the efficiency of a practical quantum key distribution system

Abstract

The performance of a practical quantum key distribution (QKD) system is often limited by the multi-photon state emission of its source and the dark counts of its detectors. Here, we present two methods to improve its performance. The first method is decoy state QKD: the sender randomly sends out weak coherent states with various average photon numbers (which are named as signal state and decoy states). In [14,15], we have performed the first experimental implementation of decoy state QKD over 15km and 60km respectively, thus dramatically increasing the distance and secure key generation rate of practical QKD systems. Our work has been followed up by many research groups worldwide [16-18]. The second scheme is QKD with "dual detectors" [19]: the legitimate receiver randomly uses either a fast (but noisy) detector or a quiet (but slow) detector to measure the incoming quantum signals. The measurement results from the quiet detector can be used to upper bound the eavesdropper's information, while the measurement results from the fast detector are used to generate a secure key. We applied this idea to various QKD protocols. Simulation results demonstrated significant improvements in both BB84 protocol with ideal single photon source and Gaussian-modulated coherent states protocol.